For all watches compatible with Firmware 4.3:
Reminders for iOS. Jog your memory with voice reminders that save to your Timeline and sync seamlessly with the iOS Reminders app. Reminders created on the watch will show in your default Reminders list on the phone. Marking items done on the watch will sync to your phone, and vice versa. Enable this Sneak Peek feature in the Pebble app » Settings » Actionable Notifications. For now, works with English-speaking users rocking Pebbles paired with iPhones.
Kickstart your day. Hop to it with Kickstart, a new default design in the Watchfaces tab of the mobile app.
For Developers. Get the full rundown at developer.pebble.com.
Compatibility. Pebble Firmware 4.3 works with 2-Series (Pebble 2) and Time-Series (Pebble Time, Time Steel, Time Round) Pebble watches. Version 3.12.3—released today—is the most current firmware for Classic-Series (Pebble Classic, Pebble Steel) models at this time.
Bug fixes and performance improvements.

For 2-Series watches:
Heart Rate Zones. Enjoy weekly charts on-wrist and in-app, tallying how much time your body’s spent in Fat Burn, Endurance, and Performance heart rate zones.
Heart Rate Over Bluetooth. Third-party phone apps can now use Pebble’s heart rate monitoring to capture, sync, and visualize pulse info during activities. Try it out today with Runkeeper!
Workouts with Heart Rate. Fitness apps that automagically send live workout data to your wrist can now include heart rate data from the watch in their visualizations.
Improved Heart Rate Monitoring. Gotta <3 that!

Pebble App for iPhone 4.3 Release Notes

For watches compatible with Firmware 4.3 and up:
Hop to it with Kickstart, a new default design in the Watchfaces tab of the mobile app.
Reminders Sneak Peek. Jog your memory with voice reminders that save to your Timeline and sync seamlessly with the iOS Reminders app. Reminders created on the watch will show in your default Reminders list on the phone. Marking items Done on the watch will sync to your phone, and vice versa. Enable this Sneak Peek feature in Settings » Actionable Notifications. Works with English-speaking users rocking Pebbles paired with iPhones for now.

For 2-Series watches running Firmware 4.3 and up:
Heart Rate Zones. See your Weekly Intensity Zones in the Health tab and on your watch. Tally how much time your body’s spent in Fat Burn, Endurance, and Performance.